Optical recording mediums, such as compact disks ("CD"), have been widely used to record audio, video, and computer data. However, some optical recording mediums, such as laser discs ("LD") and digital versatile discs ("DVD") require much larger storage capacity than currently provided by CDs in order to record digitized audio and video information of full-length feature movies, for example. One way of increasing the storage capacity of optical recording mediums is by bonding two or more optical recording medium substrates together.
Typically, the recording substrates of these multi-layered optical recording mediums are bonded together by materials that are curable when exposed to ultraviolet ("UV") radiation. First, UV bonding material is applied between two or more optical recording medium substrates. Then, the multi-layered optical recording medium is exposed to a UV radiation source to complete the bonding process. Currently, wideband sources of UV light are used to bond these multiple layers of optical recording medium substrates together.
As shown in FIG. 1, one prior art system includes a UV light source 20 and a double substrate disc 22 to be bonded. In order to bond the two substrates of disc 22, UV light source 20 irradiates the entire surface of double substrate disc 22 for the bonding to take effect.
As shown in FIG. 2, another prior art system includes a UV light source 20, a slit 24, and a double substrate disc 26 to be bonded. In this system, UV radiation from UV light source 20 is passed through slit 24. Consequently, only a line of UV radiation 28 is exposed onto double substrate disc 26. Therefore, double substrate disc 26 is rotated either clockwise or counter clockwise to expose the entire surface of double substrate disc 26 to the line of UV radiation 28.
Currently, wideband light sources, such as mercury fusion lamps are used as the UV light source of the prior art systems. Wideband light sources are difficult to spectrally control and generate large amounts of infrared ("IR") energy. Although optical filters are used to adjust the resulting spectrum reaching the substrates of multi-layered optical mediums, large amounts of heat are produced in the substrates that can cause warpage. Furthermore, longer curing times are necessary with wideband UV light sources.